This invention relates to a steam injection process for oil recovery. More particularly, it relates to an improved method of injecting a gas or vapor into a subterranean reservoir formation in which it is desirable to inject such a gaseous fluid, preferentially into a selected portion of the reservoir.
Numerous procedures have been proposed for steam soaking reservoirs. The prior proposals include patents such as the following: U.S. Pat. No. 3,354,958 describes a steam soak process using a packer to seal the annulus between concentric tubing and casing strings above perforations in the casing string. Such a preferential injection of steam into the lower portion of the reservoir depends on good seals between the packer, casing and reservoir. U.S. Pat. No. 3,410,344 describes a steam soak process conducted without a packer by pressurizing a column of foam within the annulus between the tubing and a perforated casing so that the location of the steam injection is determined by the depth of the column of foam. This tends to be difficult and expensive since the location of the bottom of that column is difficult to detect and is susceptible to wide variations in response to small variations in the pressures of the steam or foam. U.S. Pat. No. 4,445,573 describes a steam soak process which is conducted without a packer by effecting a prior or concurrent injection of a noncondensible gas foam to preferentially plug the most permeable zones in the reservoir before they are entered by significant proportions of steam.